The evaluation of five coated and noncoated grass species for the rehabilitation of gold and platinum mine tailings in South Africa

Abstract

Land use and, more recently, land rehabilitation has historically been, and remains, a key driver in the economic growth of South Africa. Environmental legislation as well as the involvement of all spheres of government and the private sector are key to the development and execution of successful rehabilitation and land use implementation action. This remains a strategic bargaining method for those in power as natural resources are directly linked to financial wealth in the current economic climate. The value of land stretches beyond the financial realm – it includes different attributes, adds to each person‟s life in a different way, and has a critical role in a sustainable ecosystem. Rehabilitation of degraded land therefore should not be a difficult choice, but a simple personal choice for each individual, but more importantly for mining houses and environmental government institutions as the principal guardians of our natural resources and a principal driver in the process of resource management. To ensure truly successful rehabilitation, scientific research has developed best-practice guidelines and methods to improve the chances of land use capability – for this study, especially in the post-mining landscape. A major role during rehabilitation of gold and platinum mine tailings storage facilities (TSFs) is played by the vegetation established. To form a sustainably biodiverse ecological community, quality preparation of soil is critical, viable seed need to be sourced and environmental factors have to be minimised in some cases and maximised in other. AGT Foods Africa (Pty) Ltd (Krugersdorp, South Africa) is a major role player in the provision of quality seed (>80% viable) to the international market. They are innovative in the production of coated seed for improved performance in adverse climatic landscapes. These “enhanced” seed provide a variety of benefits such as improved seed handling, improved biomass in agricultural uses, seed protection against various factors and the availability of short-term microenvironment plant-available nutrients for each seed. AGT Foods has been involved with research in conjunction with the North-West University since 2007 to better understand the impact of seed coating on germination and establishment of different species. The results obtained from these studies have allowed further research to take place and new ideas to come to the fore, which will ultimately empower rehabilitation specialists and the seed industry as a whole for the successful implementation of rehabilitation techniques in South Africa. The objective of this study was to investigate and compare five coated and non-coated species, chosen from the results of previous studies, funded by AGT Foods, on gold and platinum mine TSFs under dryland conditions. Thereby consolidating previous results from laboratory and nursery research into practical attempts at best-practice rehabilitation techniques. The species were evaluated based on germination, growth and survival over two growth seasons and compared in terms of species frequency and population density combined with soil analysis over time. The species chosen from previous studies were Cynodon dactylon, Eragrostis curvula, E. tef, Medicago sativa and Sorghum sp. (forage sorghum). All five species were sown onto gold and platinum tailings material on existing TSFs and monitored over two growth seasons after the soil had been ameliorated, as is common practice and required for successful establishment of vegetation in the rehabilitation industry. The seed were supplied by AGT Foods, who had tested the viability of each batch to be >80%. Some of the trials were left without mulch cover to ascertain the importance thereof when compared to mulch-covered plots. In all of the trials, the seed germinated well and established successful vegetation stands over the two growth seasons. The plots left without mulch showed very little germination initially and were covered by opportunistic rye grass (possibly transported via the compost used) for the first growth season. Thereafter, the species mix sown for the research trial revived completely to outgrow some of the other established trials. This proved that viable seed remained in the seedbed and were able to germinate even after long periods of dormancy in acidic gold TSF material. Coated E. curvula and C. dactylon performed better than non-coated seed of the same species in some cases; M. sativa and Sorghum sp. performed similarly between coated and non-coated trials. Perhaps what counted most in favour of coated seed was the fact that non-coated seed contained approximately 50% more seed per kilogram than coated, but the performance of coated seed remained similar or slightly better than that of non-coated seed. Furthermore, interesting relationships between different species and soil nutrient availability were observed and created the opportunity for seed coating enhancement to be tailor-made for certain soil factors or locations. Coated seed of E. curvula, C. dactylon, E. tef, M. sativa and Sorghum sp. are suitable for rehabilitation practices and, if sourced from a reputable seed producer, could improve the turnaround times for successful mine closure projects.